However, Oct. 16 marked a turning point in stock markets' fortunes, with the Dow Jones rising around 8 percent between that date and Oct. 31.

"I went neutral on stocks and I actually turned quite bearish for a couple of days – clearly that was wrong," Gartman told CNBC on Monday. "Whether I like to say it or not, it's still a bull market… I was wrong."

Over the year to date, Gartman said his investments were up around 8.3 percent, but added: "I should be up a lot more than that."

Fears of a bear market came ahead of the U.S. Federal Reserve's decision to halt buying up bonds – which it confirmed last week. Between Wednesday and Friday's close, the Dow Jones rose over 2 percent, which Gartman said highlighted that investors were not concerned about the end of quantitative easing (QE) in America.

Gartman said it was "astonishing" that so many investors had failed to realize this and remained on the "absolute wrong side".

"They missed the fact that everyone else is picking up the weaponry of the ECB (European Central Bank). Japan has truly picked it up, and the ECB is going to have no choice but to pick it up," he added.

Last week, Japan unexpectedly expanded stimulus, increasing its yearly target for monetary expansion to 80 trillion yen, or $724 billion, from as much as 70 trillion yen. Meanwhile, there are growing calls for the ECB to embark on a Fed-style QE program, given the region's failure to post economic growth.

Gartman isn't the only investor predicting an upward trend in stocks, with Goldman Sachs chief U.S. strategist David Kostin last week predicting that the market could see new highs by the end of the year.

But not everyone is convinced. CNBC contributor Gina Sanchez, founder of Chantico Global, said she had a " hard time seeing a rally of that magnitude" and stressed that stock markets had already priced in an economic recovery.

Looking ahead, Gartman said he was going to buy "very simple things that are incumbent in global economic growth".

"I want to own the things that if I drop them on my foot, will hurt. I want to own metals, I want to own railroads, I want to own ships," he said, naming aluminum stocks – such as aluminum producer Alcoa – as a particular favorite.